Bad Column Offset

[tjbarr]

I am using php and postgreSQL

     line1                $uom=pg_result($result_set, $i,"unitofmeas");
     line2                 $sznotes=pg_result($result_set, $i, "size_notes");
     line3                 $mark=pg_result($result_set, $i,"mark");

I get a Warning: pg_result() [function.pg-result]: Bad column offset specified in /var/data/www/nhlink/ccdsv/searchresults.php on line 2
Any ideas?.